Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a fuel evaporative emission control system for preventing or suppressing evaporative emission of a fuel gas which is generated or produced within a fuel tank of an internal combustion engine for a motor vehicle or the like. More particularly, the present invention is concerned with an abnormality detecting apparatus for detecting occurrence of abnormality such as leakage or leak of the fuel gas in the fuel evaporative emission control system.
2. Description of Related Art
In general, in the internal combustion engine for motor vehicles or the like, it is statutorily imposed to equip the engine with a fuel evaporative emission control system with the aim of suppressing or preventing evaporative emission of the fuel gas produced within a fuel tank to the atmosphere. Incidentally, this system is also known as the fuel evaporative emission suppressing (or preventing) system.
The fuel evaporative emission control system of the type known heretofore is composed of a sensor means for detecting operation states of the internal combustion engine such as rotation speed, load state and others of the engine, a purge passage for communicating the fuel tank provided for supplying the fuel to the engine and an intake pipe thereof with each other and a canister disposed in the purge passage at an intermediate location thereof.
The canister adopted for adsorbing the fuel gas produced within the fuel tank has an atmospheric air port which can be opened to the atmosphere, wherein a purge control valve is disposed at an intermediate location between the canister and the intake pipe of the engine. An adsorbent disposed within the canister adsorbs the fuel gas on the way of flowing through the purge passage through which the fuel tank and the intake pipe are placed in communication.
Further, the fuel evaporative emission control system includes a fuel evaporative emission control means (usually constituted by a microcomputer or microprocessor) for controlling opening/closing operation of the purge control valve in dependence on the operation states of the internal combustion engine in order to sustain the fuel gas adsorbing function of the canister by preventing the adsorbent from becoming saturated.
The fuel evaporative emission control means is so designed or programmed as to control opening/closing of the purge control valve in dependence on the operation states of the internal combustion engine for causing the fuel gas adsorbed by the canister to be discharged into the intake pipe so that the fuel gas is mixed with the mixture of air and fuel to be subsequently fed to the engine. In this manner, the evaporative emission of the fuel can be avoided.
Ordinarily, in the fuel evaporative emission control system such as described above, the purge passage is constituted by a rubber hose which fluidally interconnects the canister and the intake pipe. Accordingly, if the rubber hose should be bent or collapsed, there will arise such unwanted situation that the fuel gas can not satisfactorily be introduced into the intake pipe and hence the amount of the fuel gas retained within the canister will exceed the fuel gas adsorbing capability of the adsorbent accommodated within the canister, which will naturally result in discharging of the fuel gas to the atmosphere through the atmospheric air port of the canister without the fuel gas being recirculated to the intake pipe, giving rise to a problem.
Furthermore, since the rubber hose is placed in contact with alcohol component of the fuel, there undesirably exists the possibility of the rubber hose being damaged due to corrosion. Besides, in the case where the atmospheric air port of the canister should get clogged with dusts, the rubber hose will be detached under the effect of increasing of pressure. In either case, the fuel gas will unwontedly be discharged to the atmosphere, giving rise to a problem.
For coping with the above-mentioned problems by detecting the abnormal situation such as described above, there has already been proposed an abnormality detecting apparatus which is so arranged as to detect or determine occurrence of abnormality in the fuel evaporative emission control system when the pressure prevailing within the fuel tank as detected by an associated pressure sensor exceeds a permissible maximum pressure level and/or when a predetermined pressure difference is not detected before and after changeover of the purge control valve between the opened state and the closed state. For more particulars, reference should be made to, for example, Japanese Patent Application Laid-Open Publication No. 125997/1993 (JP-A-5-125997).
With the conventional abnormality detecting apparatus disclosed in the publication cited above, it is certainly possible to detect positively and accurately the blockage of the atmospheric air port of the canister, impossibility of opening the purge control valve, damage and/or fall-off of the hose serving as the purge passage on the side of the intake pipe. It is however noted that in the abnormality detecting apparatus mentioned above, the purge rate is determined without taking into consideration the intake pressure (i.e., pressure prevailing within the intake pipe) and the remaining fuel quantity at the time point when abnormality decision enabling conditions are validated (i.e., when the conditions for enabling or allowing the decision as to occurrence of abnormality are satisfied, to say in another way). Consequently, a lot of time will be taken for determining the abnormality, being accompanied with the possibility of erroneous detection of abnormality, for the reason that smooth and speedy lowering of the fuel tank pressure upon abnormality detection is hindered by flow resistance encountered within the purge passage and a variable void volume of the fuel tank.
On the other hand, there may also arise such situation that the fuel tank pressure lowers excessively although it depends on the flow resistance within the purge passage and the void volume of the fuel tank, which may result in that the fuel tank is deformed or collapsed under the effect of excessively high negative pressure.
Additionally, it is noted that in the above-mentioned abnormality detecting apparatus for the fuel evaporative emission control system, concentration of the fuel gas which flows into the intake pipe from the canister is not taken into account in establishing the abnormality decision enabling conditions. Consequently, when the concentration of the fuel gas flowing into the intake pipe of the engine is high, there arises the possibility that the engine operation becomes out of order.
Under the circumstances, there has been proposed an abnormality detecting apparatus which includes an abnormality detecting means for detecting abnormality of the fuel evaporative emission control system on the basis of the pressure within the fuel tank (hereinafter also referred to as the fuel tank pressure) and a purge rate regulating means for adjusting or regulating the purge rate in dependence on the pressure prevailing within the intake pipe (hereinafter also referred to as the intake pressure) at the time when the abnormality decision enabling conditions are validated, as is disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 296753/1997 (JP-A-9-296753).
For having better understanding of the concept of the present invention, description will be made in some detail of the abnormality detecting operation carried out by the abnormality detecting apparatus disclosed in the publication cited just above.
of the accompanying drawings shows a flow chart for illustrating the abnormality detecting operation of the abnormality detecting apparatus now concerned.
, decision is first made in a step S
A as to whether the concentration of the fuel gas (hereinafter also referred to as the fuel gas concentration) as detected by resorting to an appropriate method (see JP-A-9-296753 for more particulars) is higher
Moulis Thomas N.
Sughrue & Mion, PLLC
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